Impact of the antenna topology on the combination of full-duplex spatial modulation and RF energy harvesting

In the context of full-duplex spatial modulation (FDSM) systems, this paper proposes a strategy that exploits the subset of antenna that is not used by the transmitter nor by the receiver to perform RF energy harvesting (RFEH). Through the mutual coupling effect, the transmitting antenna of each node transfers a part of its power to the other antennas of the array. Our idea is to recycle this power at this same node in complement to the ambient RF sources. Our study shows that the level of the available power may be greater than the RF ambient sources. The impact of the spacing d between the elements of an array of four antennas on the performance of the FDSM-RFEH was studied. For the RFEH aspect, when d is small, the harvested DC power level is greater. Contrary, for the FDSM aspect, when d is small, the level of the interference to noise ratio (INR) is greater, and the self-interference cancellation (SIC) is therefore impossible. The best compromise for the spacing is d = 0.6 lambda, where lambda is the wavelength. By analysing the transfer coefficients extracted from S-parameters simulations performed on a four patch linear antenna array, the role of each antenna (emission, reception, RF energy harvesting) may be established.